Solenoid drive apparatus for an external infusion pump

ABSTRACT

A solenoid drive apparatus for driving a lead screw of an External Infusion Pump (1) having a housing (302), solenoid winding (356) within the housing (302), a solenoid armature (358) which is driven by the field of the solenoid winding (356), push rod (362) which is driven by the armature (358), pawn (314) which is driven by push rod (362), a first pawl (320) which is driven by pawn (314) and a second pawl (326) which is an antibacklash device, a ratchet wheel (318) having teeth (319) around its periphery and engaged by the first pawl (320) and the second pawl (326) and the drive shaft (316) which is drawn by the ratchet of the ratchet wheel (318).

This is a continuation of co-pending application Ser. No. 568,615 filedon 01/06/84.

DESCRIPTION TECHNICAL FIELD

The present invention relates to the field of fluid pumping apparatusesand their method of use. In particular, the present invention furtherrelates to external infusion pump apparatuses and their method of usefor providing accurate dosages of a fluid to a user.

BACKGROUND

In the past, there have been various attempts to provide apparatuseswhich would be able to effectively simulate a malfunctioning body organand provide certain fluids to the body for control of certain bodilyfunctions. These apparatuses have been contemplated to be both internaland external. One of the largest areas for use of these apparatuses wasto control the amount of insulin input required by a diabetic.

Without such devices, the diabetic had to rely on taking insulininjection at periodic intervals to control his disease. This requiredthat the diabetic always carry around a hypodermic needle and a supplyof insulin should the need arise that dosage was required to control thedisease.

This reaction type remedy caused the diabetic to take improper dosagesof insulin to control his or her disease. It was rarely the case thatthe proper amounts of insulin were dispensed to the body as would bedone by the insulin producing organ. Although insulin is being used byway of example, the same is true for other necessary fluids that are nolonger supplied to the body in correct dosages because of amalfunctioning organ.

Previous apparatuses, used for supplying fluids to the body to replaceor supplement the fluids provided by a malfunctionining organ, werereaction type devices and not intended to essentially simulate theimproperly functioning organ.

The major drawback in reaction type-apparatuses were side effects to theuser. In a particular case of a diabetic, there could be insulin shockbecause the body would not accept large dosages of insulin.

There have been various additional problems with previous apparatuses intheir ability to change with the needs of the user. In most cases, ifthere was an automatic system, it would be set to provide a large volumeof the required fluid to the body. Essentially, the apparatus would behardwired to produce a certain output which would be unchanging. Toprevent any problems with this type of system, it was always constructedsuch that there could be no changes in volumetric delivery made by theuser. Any changes to be made in the prescription would have to be madeby the physician or required the purchase and installation of a newsystem to handle this increased or decreased volumetric need.

Such apparatuses in the past were neither programmable nor able to beaccessed and operated by the user. Since this was the case, it made theuser extremely dependent upon the physician to take care of all of hisneeds in accordance with his or her specific physiological requirements.Because of the limited time that doctors have to see any particularuser, it was difficult for the problems of the doctor to finalize theproper volumetric requirements for the user so as to prevent or minimizeany undesirable side effects.

The present invention overcomes these and other problems as will bedescribed subsequently.

SUMMARY OF INVENTION

The present invention is an external programmable infusion pumpingapparatus or fluid delivery system for providing small accurate dosagesof a required fluid to a user. This apparatus effectively simulates theperiodic and volumetric requirements of a properly functioning humanorgan to provide a particular fluid to the body of the user.

The apparatus of the invention is attached to a catheter or otherdelivery system which is inserted subcutaneously for the delivery of therequired body fluid to the user at periodic intervals.

The apparatus of the invention is extremely small in size and light inweight. It provides accurate dosages of a fluid to the user. Theapparatus has analog and digital circuitry which works in conjunctionwith a microprocessor, external memory (external from themicroprocessor) and an LCD display. The apparatus has incorporatedtherein circuitry for producing audio tones for indication of certainconditions or for warning the user of various problems that exist in theapparatus. Additionally, the apparatus has a pressure switch associatedwith a lead screw which will indicate when the fluid reservoir is emptyor when there are problems with the pump apparatus that prevents thepumping of fluid from the reservoir.

The apparatus of the invention is programmable, as stated, and itsprogramming can be changed by the physician or by the user. Theapparatus has a series of actuator means in the form of buttons whichare used to change the rate of volumetric output, concentration andmaximum level of the pumped fluid, and further to display certaininformation. Additionally, whenever changes are made to the programmingof the apparatus, the new parameter values stored in the random accessmemory (RAM) of the microprocessor are displayed. The apparatus of theinvention also has protection circuits so that if there is some problemwith the primary power source, the programming in the apparatus ismaintained. This is also true when it is necessary to change primarypower sources so that the user will not have to reprogram the apparatusafter replacement of the primary power source.

And object of the invention is to provide a programmable fluid infusionpump apparatus that can accurately dispense specific volumes and/orrates of delivery of a desired fluid subcutaneously or otherwise to auser.

Another object of the invention is to provide a programmable fluidinfusion pump apparatus havin analog and digital circuitry means foraccurately dispensing fluid to a user.

A still further object of the invention is to provide a programmablefluid infusion pump apparatus which has a means for protecting theprogramming of the apparatus when a primary power source fails or isremoved.

A still further object of the invention is to provide a programmablefluid infusion pump apparatus having a microprocessor which isinteractive with the analog and digital circuitry of the apparatusdisplaying certain information about the status of the apparatus, andfurther having an alarm means for indicating problems or certainconditions of the apparatus.

Another object of the invention is to provide a programmable fluidinfusion pump apparatus which has charge storage means for storinggenerated power for driving a pump drive means.

A still further object of the invention is to provide a programmablefluid infusion pump apparatus with a plurality of actuator means forchanging the programming of the apparatus of invention.

Another object of the invention is to provide a low level system forpumping a desired fluid to a user, and circuitry for protecting a powersource from excessive power drain.

A further object of the invention is to provide a programmable fluidinfusion pump apparatus having means for selectively engaging anddisengaging an elongated threaded member.

A primary object of the invention is to provide an electrically operatedapparatus for driving a second apparatus mechanically.

A further object of the invention is to provide an apparatus which hasthe means for automatically changing the rate of delivery of a desiredfluid to a user without user interaction.

An even further object of the invention is to provide an apparatus whichhas an alarm means to indicate when a fluid reservoir is empty or thatfluid cannot be pumped from the reservoir because of a problem with thepump mechanism.

These and other objects of the invention will be described fully insubsequent paragraphs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an elevation view of the apparatus of the invention.

FIG. 2 shows a partially cut-away view of the apparatus of the inventionalong 2--2 of FIG. 1.

FIG. 3 is a block diagram of the apparatus of the invention.

FIG. 4 shows the schematic diagram of the apparatus of the invention.

FIG. 5 shows the timing diagram for the bus control signals forthemicroprocessor of FIG. 4.

FIG. 6 shows a general flow diagram of the software of themicroprocessor of FIG. 4.

FIG. 7 shows an exploded view of the engagement/disengagement means ofthe apparatus of invention for engaging and disengaging the lead screw.

FIG. 8 shows the assembled engagement/disengagement means of FIG. 7.

FIG. 9A shows a cross-sectional view of the engagement/disengagementapparatus at 9--9 of FIG. 8 with the pump driver in the normal position.

FIG. 9B shows a cross-sectional view of the engagement/disengagementmeans at 9--9 of FIG. 8 with the pump driver rotated in a firstdirection.

FIG. 10 shows a partially exploded view of the solenoid drive means ofthe apparatus of the presently claimed invention.

FIG. 11 shows an assembled view of the solenoid drive means of theinvention shown in FIG. 10.

FIG. 12 shows a cross-sectional view of the solenoid drive means of theinvention shown at 12--12 of FIG. 11.

FIG. 13 shows a partial view of the ratchet means and pawls which engagethe ratchet means of the solenoid drive means shown in FIG. 11.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIGS. 1 and 2, an elevated view and partial cut-away viewof the apparatus of the invention is generally shown at 1 and 2,respectively. The apparatus has an outer casing 9, which housesmicroprocessor 18 and other circuitry, fluid reservoir 5, mechanicalpump drive means 300, engagement/disengagement means 220 and primarypower source 11. The fluid pumped from reservoir 5 is output throughconduit 7 which is connected to a catheter or subcutaneous insertionpoint for input to the user. The actuator means, T button 24; A button26; B button 28; and M button 30 are disposed through case 9 and usedfor changing program parameters within memory of the apparatus ordisplaying certain information on LCD 40. The relationship of some tothe components of the apparatus of the invention is shown generally inFIG. 2.

Fluid in fluid reservoir 5 is dispensed through conduit 7 to the user asstated. The fluid is forced from the fluid reservoir 5 by plunger 5'shown in phantom in FIG. 2. The end of the plunger is engaged by pumpdriver 272 of engagement/disengagement means 220 which is disposed onlead screw 292. Lead screw 292 is driven by solenoid drive means 300. Assolenoid drive means 300 causes rotation of ratchet wheel 318, leadscrew 292 is rotated in a clockwise direction causingengagement/disengagement means 220 to move along lead screw 292 towardsolenoid drive means 300, thereby forcing fluid from the reservoir intoconduit 7.

Disposed at the distal end of lead screw 292 is high pressure switch 7'.The distal end of lead screw 292 has reduced portion 293 which has arounded end. This reduced portion 293 is received through bearing 295 inan inside casing wall and the rounded end of reduced portion 293contacts the high pressure switch 7'.

Once engagement/disengagement means 220 travels the length of lead screw292 and all of the fluid has been pumped from fluid reservoir 5, plunger5' will have traveled its full distance within fluid reservoir 5 andengagement/disengagement means 220 can no longer move in a directiontoward pump drive means 300. Any further turning of lead screw 292 bypump drive means 300 will cause lead screw 292 to move in an axialdirection toward pressure switch 7'. The rounded end of reduced portion293 will be driven into high pressure switch 7' causing the switch toclose. The appropriate alarm condition will be set.

Switch 7' will also be closed if plunger 5' becomes fouled and cannot bemoved into fluid reservoir 5. In this case, lead screw 292 will again bedriven toward high pressure switch 7' and the switch will be closed asstated. Again the appropriate alarm condition will be set.

Referring to FIG. 3, a block diagram of the apparatus of invention isgenerally shown at 3. The main control means for operation of theapparatus of the invention is microprocessor 18. The other components ofthe apparatus are connected to microprocessor 18 serving either input,output or memory functions.

The apparatus in general is powered by primary power source 11. Primarypower source 11 usually consists of three 1.5 volt silver oxidebatteries connected in series providing approximately 4.5 volts to powerthe system. Auxiliary power source 4, which is connected to auxiliarypower source assistance circuit 6 is used in two situations. The firssituation is when primary power source 11 falls below a certain voltagelevel below which the primary power source can no longer adequatelypower the apparatus. The second situation is when the primary powersource is being replaced. In each case auxiliary power source 4 providesenough voltage to the apparatus to maintain the RAM of microprocessor 18so that programming is not lost.

Auxiliary power source assistant circuit 6 is connected between theauxiliary power source and the system power supply line. The mainpurpose of this circuit is to provide a voltage to put the apparatus ina sleep state and supply enough voltage to maintain RAM ofmicroprocessor 18.

The primary power source has means connected to all of the operablecomponents of the apparatus. The auxiliary power source on the otherhand is so situated in the circuit that it will provide the power to theentire apparatus but the apparatus is in a sleep state so power isprovided to maintain RAM and not generally to the apparatus to make itoperable.

Power generation circuit 8 is connected to primary power source 11 andmicroprocessor 18 and when powered, generates the proper power levelsfor driving pump drive mechanism 12 for operating pump 14. Powergeneration circuit 8 is disposed between primary power source 8 andpower storage circuit 10.

Power storage circuit 10 receives the output from power generationcircuit 8. A charge is built up and stored in circuit 10 until apredetermined voltage level is reached, at which time the powergeneration circuit is turned off. This voltage is stored in circuit 10until it is delivered to pump drive mechanism 12.

Sensing system 16 is connected to primary power source 11, pump drivemechanism 12 and microprocessor 18. Sensing system 16 is used for twopurposes. First, it senses when the primary power source voltage fallsbelow a predetermined level, and second it senses when the storagecircuit is charged to a certain voltage level. In conjunction withsensing the conditions of the storage circuit, it senses when voltagehas been delivered from power storage 10 circuit to pump drive mechanism12. Sensing system 16 inputs its sensed conditions to microprocessor 18for carrying out the necessary internal apparatus functions indicativeof the conditions that are sensed.

The operating software subroutines for operation of the apparatus arestored in a read only memory (ROM) 34. This memory is connected tomicroprocessor 18, address latch 36, power source 11, and memory enablemeans 32. The other memory of the apparatus is the RAM of microprocessor18 which stores the present programming parameters for operation of theapparatus.

Once the proper parameter is in RAM, the apparatus will function inaccordance with these parameters. Microprocessor 18 acts on theseparameters stored in RAM and processes them in the subroutines stored inmemory 34.

An oscillator internal to microprocessor 18 uses a 32768 Hz crystalwhich is divided down and provides proper clock timing for the apparatusof invention.

In order to display certain information, microprocessor 18 is connectedto LCD driver 38 which in turn provides discrete outputs to LCD 40. Byproper actuation of either T button 24; A button 26; B button 28; and/orM button 30 or combinations thereof, LCD 40 will display the desiredinformation.

An additional feature of the apparatus is that tone transducer 22provides audio tones to indicate certain alarm conditions or to indicatethe occurrance of certain functions.

Referring to FIG. 4, analog circuitry, digital circuitry and certaincomponents of the apparatus of invention are generally shown at 50. Theapparatus is powered by primary power source 52.

The auxiliary power source is battery 60. This battery is a 3.1 voltlithium battery. The two power sources are so situated that the anodesor positive terminals of primary source 52 and auxiliary source 60 areconnected to each other through a diode 68 on V+ line 69. When primarypower source 52 is present, diode 68 is forward biased on the directionof auxiliary power source 60 on V+ line 69. This reverse biases Schottkydiode 66 taking auxiliary power source 60 out of the circuit. The uniqueutilization of these two power sources will be described subsequently.

Primary power source 52 is used for generating the necessary voltage foroperation of the apparatus. Auxiliary power source 60 is used forsupplying voltage to RAM of microprocessor 18 when, for some reason,primary power source 52 is missing or inoperable. Associated with thesetwo power sources are reference voltages V-1, 62 and V-2, 64 which areused in various places throughout the apparatus. A description of thesereference voltages will follow in this disclosure.

When the primary power source 52 is present, diode 68 is forward biasedas stated. When this is the case, there is approximately a 0.5 voltagedrop across diode 68 and diode 66 is reversed biased. Therefore, theresultant voltage at V-1, when source 52 is present, is 4.5 volts minusthe 0.5 volt drop across diode 68 and minus the voltage of auxiliarypower source 60, which is 3.1 volts. So, V-1, 62 will be approximately0.9 volts.

Schottky diode 66 has its anode connected to the cathode of battery 52.The cathode is effectively at a zero voltage. Since V-1 is at 0.9 volts,this verifies Schottky diode 66 is reversed biased. V-1 will remain at0.9 volts as long as source 52 is present. Schottky diode 66 will remainreversed biased as long as V-1, 62 has a positive value.

Voltage V-2, 64 is a divided down voltage of primary power source 52.The voltage of V-2 is dependent on the relationship of resistors 54 and56. As will be explained, the V-2 reference voltage has an effectivepositive value only when primary power source 52 is in the circuit,otherwise it is near zero volts.

When primary power source 52 is removed, the only power source isauxiliary power source 60, the 3.1 volt lithium battery. When this isthe case, diode 68 is reversed biased. The direction of current flow isfrom the anode of power source 60 to the circuit and back through groundthrough Schottky diode 66 to the cathode of battery 60. By this method,Schottky diode 66 is forward biased. Because of the current flow, thevoltage at V-1, 62 will be one Schottky diode voltage drop, which isapproximately 0.3 volts below common reference voltage (zero volts) online 71. Also, since primary power source 52 is not in the circuit V-2,64 is at or near zero volts.

When primary power source 52 is removed and auxiliary power source 60provides the voltage of V+ line 69, this is sensed by microprocessor 18.When this takes place, microprocessor 18 will put the apparatus in asleep state. When the apparatus is in this state, the bit pattern of RAMof microprocessor 18 is maintained.

In order to assist the auxiliary power source 60, capacitor 84 depletesits charge to V+ line 69. Also the action of inverter 78 and FET 72 andcapacitor 74 assists in elevating the effective supply voltage to theapparatus.

In this case, the anode voltage of primary power source 52 is considereda logic "1" value and the cathode voltage is a logic "0" value. Whenprimary power source 52 is present, the input to inverter 78 is a logic"1" value which causes the output of the inverter 78 to assume a logic"0" value. This logic "0" value is input to the gate of field effecttransistor (FET) 72, rendering it in an off condition. When primarypower source 52 is removed, the input to inverter 78 is a logic "0"value, so, the output of inverter will assume a logic "1" value, whichis input to the gate of FET 72 and turns it on. When this FET is turnedon, it will cause shorting of the voltage at V-1 to ground. This willessentially short Schottky diode 66 to ground lessening the effect ofthe voltage drop across the Schottky diode. The voltage drop will changefrom a 0.3 volt drop to a 0.1 volt drop. This effectively adds 0.2 voltsto the circuit on V+ line 69.

When the primary power source is in place, power for infusion pump drivemechanism 12 is generated by power generation circuit 8 (FIG. 1). Thewindings 86, 88 and 90, along with FETs 92, 94, and 96 form a fly-backcircuit. The fly-back circuit is enabled by microprocessor 18 on line33.

When it is desired to generate the voltage necessary for running pumpdrive mechanism 12, a positive voltage is supplied to winding 86 vialine 33. This bias voltage is supplied to the gates of FETs 92, 94 and96 after passage through winding 86. Once the enable signal is providedthrough windings 86, the three FETs are turned on and the V+ signalprovided to winding 88 completes a circuit to common ground 71 throughFETs 92, 94 and 96. Winding 88 then produces a varying field thataffects windings 90 and 86. This varying field will cause an inducedvoltage to appear in windings 90 and 86. The negative feedback fromwinding 88 to winding 86 causes the FETs to effectively cut off. Thisbreaks the circuit in primary winding 88 and causes the opposite varyingfield in winding 88.

Winding 90 is affected by also varying field of winding 88. Since thecycle is as described, winding 90 has an output which is oscillating.These oscillations appear as an AC signal in line 97. This AC signal isrectified by rectifier 98 and a pulsatory DC current is provided to thecapacitor bank consisting of capacitors 100, 102, 104, 106, 108, 110 and112.

Again referring to FIG. 4, the capacitor bank is power storage circuit10 in FIG. 3. It will take approximately five seconds for the fly-backcircuit to charge the capacitor bank to the proper level. Once thepredetermined charge level of the capacitor bank is reached, thefly-back circuit will be disabled by removing the enable signal fromline 33. Since the circuit includes zener diode 114, silicon controlledrectifier (SCR) 118 and diode 98, the charge on the capacitor bankremains on the capacitors until other operations take place which willcause it to be delivered to pump drive mechanism 12 as will be describedsubsequently.

In order to determine when the proper charge is on the capacitor bank,comparator 124 of sensing system 16 is used. V-1 signal 62 is directedto the inverting input and the voltage on line 115 is directed to thenon-inverting input. Line 115 is also connected to the capacitor bankthrough pump mechanism 12 and zener diode 114.

As the charge is being built up in the capacitor bank, it is applied tozener diode 114 in the reversed direction. Zener diode 114 will breakdown at a certain voltage level. When this break down takes place, thevoltage value at the non-inverting input to comparator 124 willincrease.

In order to provide voltage level to comparator 124 via line 115,resistor 116 is placed in a circuit so that there will be a voltage dropacross it. As the breakdown of zener diode 114 takes place, the voltagelevel, caused by the voltage drop across resistor 116, will cause a risein the voltage at the non-inverting input of comparator 124. As thevoltage applied to the non-inverting input of comparator 124 reaches avalue greater than the value of V-1 62, the logic output of comparator124 will change from a logic "0" value to a logic "1" value which isinput input to microprocessor 18 via line 29. This logic "1" valuesignal on line 29 will cause microprocessor 18 to stop the output of theenable signal on line 33 for running the fly-back circuit previouslydescribed. Thus, the fly-back will be turned off and the proper level ofstored charge is available in the capacitor bank for driving pumpmechanism 12. Once charge is stored in the capacitor bank, the batteryor primary power source 52 is no longer used for the fly-back chargingcircuit.

In order to deliver the charge stored in the capacitor bank to the pumpdrive mechanism, a signal must be received from microprocessor 18. Whenthe software of the apparatus of invention determines that a pump strokeis needed the above charging sequence is completed and a fire signal isinput to SCR 118 as a logic "1" signal via line 31. This signal willturn the SCR on and connect the output of pump drive mechanism 12 toground. This provides a path for delivering the charge stored in thecapacitor bank to the solenoid winding in pump drive mechanism 12. Thepump drive mechanism is a magnetic solenoid type apparatus. When thecharge is delivered, it will cause pump drive mechanism 12 to drive thepump and cause pumping of the desired fluid to the user.

The apparatus of invention checks to see if the charge time for thecapacitor bank takes less than one second. If less than a secondcharging time takes place, the apparatus will recognize a false chargingcondition and will assume that there is a dead battery condition. Thisis one method to determine if the primary battery is dead.

The method in which a low battery condition is sensed is by use ofcomparator 122. This comparator has inputs from V-1 signal 62, which isinput to the inverting input of comparator 122, and V-2 signal 64, whichis input to the non-inverting input of comparator 122. The circuit is soconfigured that the initial condition V-1 signal 62 is greater than V-2signal 64. As primary power source 52 has its charged depleted, V-1 willdecrease faster than V-2. V-1 will fall below the V-2 at the point whichis indicative of a low battery condition. Therefore, when the lowoperating point is reached, the output of comparator 122 will be a logic"1" value which is input to microprocessor 18 via line 27. There will bea display of this condition on LCD 40. This will also cause an output bytone transducer 22, after processing by the logic circuitry comprised ofNOR Gate 128, capacitor 131, resistor 130 and 132 and NOR Gate 134 ofthe signal output microprocessor 18 on line 17. The actual operation ofthis circuitry will be described subsequently.

Again referring to FIG. 4, the method of driving tone transducer 22 isaccomplished by microprocessor 18, NOR Gate 128, capacitor 131,resistors 130 and 132, and NOR Gate 134. NOR Gate 134 is the controllinggate for providing an input tone transducer 22. NOR Gate 128, capacitor131, resistor 130 and resistor 132, comprise a self oscillating R/Ccircuit.

The output on line 17 from microprocessor 18 is normally a logic "1"value. When the output is desired from tone transducer, the output frommicroprocessor 18 on line 17 is a logic "0" value. Since the normaloutput is normally a logic "1" value, the output of NOR Gate 134 is alogic "0" value regardless of the condition of the self-oscillatingcircuit. When both inputs to NOR Gate 134 are logic "0" values, theoutput will be a logic "1" value. This will take place when a logic "0"value is output from microprocessor 18 on line 17 and when the output ofthe oscillator circuit is a logic "0" value. The logic "1" value outputof NOR Gate 134 causes the oscillator circuit to oscillate between alogic "0" and a logic "1" each time the oscillator output assumes alogic "0" value. The tone transducer 22 will receive the oscillatingsignal and provide an audio output as per the logic "1" value output ofNOR Gate 134.

The actuator means previously described are T button 30, A button 24, Bbutton 26 and M button 28. These buttons connect to microprocessor 18through connector board 55. The buttons are used for various functions.The main purpose of the buttons are to change program parameters and tocause the display of parameter values on LCD 40. A description of thebuttons will be set forth subsequently.

The apparatus as previously indicated has a high pressure switch whichis used to indicate when the fluid reservoir is empty, or when there isa problem with the pump mechanism such that plunger 5' (FIG. 1) cannotbe driven into fluid reservoir 5 (FIG. 1), or when no fluid is beingpumped when pumping is directed.

Referring to FIG. 4, high pressure switch 103 has a first terminalconnected to the input of pump drive mechanism 12 through resistor 101and a second terminal connected to ground. When the switch 103 isopened, the apparatus operates in the normal manner: the fly-back willcharge the capacitor bank; and, when a fire signal is output frommicroprocessor 18 to SCR 118, the charge on the capacitors will bedelivered to the pump drive mechanism 12.

However, when fluid reservoir 5 (FIG. 1) is empty or plunger 5' (FIG. 1)is obstructed and cannot cause pumping of fluid from the fluidreservoir, high pressure switch 103 will be closed as previouslydescribed. When this happens, line 97 (which is input to pump drivemechanism 12) and the capacitor bank are shorted to ground throughresistor 101 and high pressure switch 103. Therefore, once switch 103 isclosed, when the fly-back circuit is enabled to charge the capacitorbank, the current induced in winding 90 will be shorted to ground. Therewill not be charging of the capacitor bank so the output of comparator124 will not assume a logic "1" value within the time window forcharging the capacitor bank once the fly-back is enabled.

If the capacitor bank, as seen by capacitor 124, is not charged to theproper level within approximately 12 seconds, microprocessor 18determines that there is a problem with the apparatus. Microprocessor 18enters an alarm state indicating the apparatus is not pumping fluid whendirected. The alarms associated with this state are both audio andvisual (on the LCD).

Actuation of the buttons will interrupt the normal operating routine ofthe microprocessor. The change in programming caused by actuation of thebuttons will affect the operation of the apparatus. This interrupt iscaused through FET 138.

When the primary power source is in place, the gate of FET 138 receivesa positive gate voltage and the FET is turned on. When this takes place,pull-up resistor 136 will be defeated causing a logic "0" value at point135 when one or a combination of buttons are actuated. This logic "0"value is input to microprocessor 18 via line 37. This input on line 37will cause scanning of the button I/O lines 19, 21, 23 and 25 bymicroprocessor 18. Once microprocessor 18 determines which button orbuttons have been actuated, it will take appropriate action and updatememory with a new parameter value and/or cause the microprocessor tooutput from memory certain parameters which will be displayed on LCD 40.

The timing for the apparatus is carried out by a 32768 Hz clock usingcrystal 148. The frequency is divided down internally by themicroprocessor and causes proper timing for apparatus.

The apparatus of invention has certain safeguards which are necessary toprevent inadvertent or unauthorized changing of the program parametersfor the user. The main safeguard is that there is a circuit external tomicroprocessor 18 that must be activated before certain programming,e.g., setting maximum limits for the apparatus. The circuit contains aswitch which must be closed before such changes can be accomplished.

Referring to FIG. 4, reed switch 159 is normally in an open condition.One terminal of reed switch 159 is connected to a V+ voltage throughpull-up resistor 157 and to I/O port line 161. The second terminal ofreed switch 159 is common ground 71.

In the open condition, the voltage on line 161 is a logic "1" value.However, when an external device causes reed switch 159 to close, thevoltage in line 161 will assume a logic "0" value and enablemicroprocessor 18 to receive the desired new programming.

Again referring to FIG. 4, the apparatus is configured so that the sameinterconnecting lines between microprocessor 18, address latch 36 andmemory 34 are used as a multiplexed address bus and data bus. The timingand circuitry of the apparatus of invention are set up so that duringthe period that the interconnecting lines used as the address bus,memory 34 is disabled so that there is no data output on theinterconnecting lines. Likewise, when the data is being output frommemory 34 and the lines are used as the data bus, address latch 36latches the previous address and the address latch is not affected byinformation from the data bus.

In order to carry this out, there must be an explanation of the logiccircuitry (referred to as memory enable circuit 32 in FIG. 3) involvingNOR Gate 158, NOR Gate 156, and flip-flop 162. In conjunction withdescribing the logic circuitry, the timing diagrams for bus controlsignals of microprocessor 18 will be described.

Referring to FIG. 5, the timing diagrams AS signal for 410, DS signal430, and R/W signal 440 are shown generally at 400. These are the buscontrol signals from microprocessor 18. The cycle period is labelledtime "t". The relationship between AS signal 410, DS signal 430 and R/W440 is shown.

Referring to FIGS. 4 and 5, at the beginning of the cycle, when DSsignal 430 has a logic "0" value, it is input to the tied inputs of NORGate 158 via line 15. This causes the output of that logic gate toassume a logic "1" value, which is input to flip-flop 162. This logic"1" value signal will reset flip-flop 162 and the Q output of flip-flop162 will assume a logic "1" value. This logic "1" value is input to thechip enable (CE) and output enable (OE) inputs to memory 34. Since theCE and OE inputs are negative/true, the logic "1" value input to eachwill render chip 34 disabled and no outputs will be available frommemory 34. At the same time, AS signal 410 with a logic "1" value isinput to address latch 36. This input allows address latch 36 to receiveinputs from the address bus lines.

Continuing through the cycle of period "t", R/W signal 440 assumes alogic "1" value prior to AS signal 410 assuming a logic "0" value at414. When R/W signal 440 assumes a logic "1" value, the input to the Dinput to flip-flop 162 changes from a logic "0" value to a logic "1"value. The clock signal for flip-flop 162 is the output of NOR Gate 156.The inputs to NOR Gate 156 are tied and the output of oscillator circuitof crystal 148 previously described. When the oscillator circuit outputtransitions from a logic "1" value to a logic "0" value, the output ofNOR Gate 156 will change from a logic "0" value to a logic "1" value.The positive edge will clock flip-flop 162. However, since DS signal 430remains a logic "0" value at 432, flip-flop will remain reset and theclocking of flip-flop 162 will have no effect on the Q output offlip-flop 162.

When the timing of the cycle reaches the point where DS signal 430assumes a logic "1" value 434, the output of NOR Gate 158 will assume alogic "0" value which is input to the reset input of flip-flop 162. Whenthis happens, flip-flop 162 will no longer be held reset. Since R/Wsignal 440 is a logic "1" value at 444, the logic "1" value loaded intothe D input of flip-flop 162 will upon clocking cause the Q output offlip-flop 162 to assume a logic "0" output. This logic "0" value isinput to the CE and OE inputs of memory 34 which are both negative/trueinputs. This will enable the memory and cause outputs from memory 34.The lines are now used as data bus lines for input to microprocessor 18from memory 34. Therefore, the output from memory 34 input tomicroprocessor 18 for processing in accordance with the softwarecommands. Just prior to this action, the AS output 410 transitions to alogic "0" value which causes latching of the address values. Thesevalues are supplied to memory 34 via address lines during the dataretrieval interval.

Referring to FIG. 4, the components of the apparatus of invention haveinputs to connector board 55. This connector board processes theinformation and provides inputs to LCD 40 to display certain informationindicative of the inputs to connector board 55.

Referring to FIG. 6, a flow diagram of the software of the apparatus ofthe invention is shown at 170. The apparatus of invention operates ontwo levels. The first level is a sleep state and the second level is anactive state. The apparatus operates in these two states to conserve thebatteries and give them extended life.

The timing for the apparatus is controlled by quartz clock 172. Thebasic operation of this low level system centers around the interruptroutine 174 having 5 second wait subroutine 176 contained therein. Theapparatus is constructed so that the apparatus will be woken up every 5seconds to check certain conditions, update the apparatus clock, controlthe output functions of the apparatus and return to the sleep state.This 5 second time period is the minimum inactive interval for theapparatus. The only actions which can take place outside of the 5 secondwake up subroutine are caused by actuation of the buttons causing theapparatus to shift to an "active" state thereby invoking main buttonpattern recognition subroutine 200, or to reset the battery test IRQinterrupt subroutine 177 which is generated each time the battery testroutine 182 is entered. These two interactive portions of software willbe described.

Again referring to FIG. 6, when the subroutine associated with mainbutton pattern recognition 200 is initiated, by actuation of one or acombination of buttons, the apparatus leaves the 5 second waitsubroutine and enters the main button pattern recognition subroutine 200to determine which button has been actuated and take the appropriateaction. The buttons can be actuated alone or in combinations. Eachsubroutine associated with button activation will be describedsubsequently.

When M, B and T buttons are actuated simultaneously, the main buttonrecognition pattern is entered. When the button pattern is recognizedthe apparatus will enter concentration subroutine 214. When thishappens, the concentration of the fluid in the fluid reservoir (notshown) will be displayed on LCD 40. If this is the only buttonactuation, a short period of time after release of the buttons of theapparatus will return to the 5 second wait subroutine. If it is desiredto change the concentration of the fluid being pumped to the user first,the reed switch must be closed by an external device, when the M, B andT buttons are actuated again simultaneously. The concentration of thefluid will again be displayed on the LCD. The B button must be actuatedto change to the desired concentration. When the desired concentrationis reached, the A button is actuated which will store the newconcentration parameter value in memory. A short period of time afterstorage of the new parameter value, the apparatus will return to the 5second wait subroutine 176. This action will also cause all previousprogram parameters to assume zero values.

When the A and T buttons are actuated simultaneously, the apparatus willenter the main button recognition pattern 200. After this button patternis recognized, the apparatus will enter the level subroutine 212. Thisresults in a display indicative of the units of fluid remaining in thefluid reservoir. A short period of time after release of the buttons,the apparatus will return to a 5 second wait routine 176.

It is always necessary to restore the apparatuses full fluid levelcondition every time a new fluid reservoir is placed in the apparatus.This is done by actuating the A and T buttons simultaneously, releasingthe A and T buttons and reactuating and holding the A button until thefull level is indicated. When this value is indicated, the A button isreleased and the full value is stored in memory. The apparatus will thenreturn to a 5 second wait subroutine 176.

When the M and B buttons are activated simultaneously, the apparatuswill enter the main button pattern recognition routine 200. After thebutton pattern is recognized, the apparatus will enter total subroutine210. The total value is the amount of fluid in units pumped from thefluid reservoir since the previous midnight. This amount will bedisplayed on the LCD. After a short period of time, the apparatus willreturn to 5 second wait subroutine 176.

When the apparatus is in the total subroutine 210 and the A button isactuated, the apparatus will go into a standby mode. In this mode, theapparatus is powered but no internal function takes place other thantimekeeping and maintaining RAM. This is used, when the user may wish todisconnect the apparatus to take a shower or other similar action wherethere is no need for the apparatus of invention for an extended periodof time. When this activity is over, the M and B button actuation isrepeated and the apparatus returns to the total subroutine 210. Afteractuation of the A button, the apparatus will return to normal operationwithin 5 second wait routine 176.

When the T button is pressed alone, the apparatus will enter the timeset subroutine 208, which is used for setting the time, afterrecognition by main button pattern recognition subroutine 200. The timewill be displayed on the LCD by this first activation. To correct thetime, the T button is actuated until the proper time is displayed. Afterthis, the A button is actuated to store the new parameter in memory andthe apparatus will return to the 5 second wait routine 176.

When the B button is actuated alone, the apparatus will enter the mainbutton pattern recognition subroutine 200 and then basal rate subroutine204. This basal rate will then be displayed on the LCD. If nothing elseis done, after a period of time, the apparatus will return to 5 secondwait routine 176. If it is desired to change the basal rate, the Bbutton is held in the activated position and the basal rate value willincrease. When the desired value is reached, the button is released andthe A button is activated which stores the value in memory and theapparatus will return to 5 second wait routine 176.

There are a maximum of four basal rate profiles into which any 24 hourperiod can be divided. In order to index to any specific profile the Tbutton is used. Once in one of the basal rate profiles indexing tosubsequent profiles is carried out by actuating the T buttonsuccessively. When the desired profile is checked or changed, theapparatus will return to the 5 second wait routine 176 after release ofthe A or T button depending on whether the basal rate profile waschanged or checked, respectively. The reed switch must be actuated inorder to change both the time and rate parameters of a basal profile.Otherwise, only the rate parameter can be changed. No permanent changeto any basal rate is accomplished unless stored by actuation of the Abutton.

When the M button is actuated alone, as with the other buttons, the mainbutton pattern recognition subroutine 200 is entered and then the mealbasal rate subroutine 202 is entered once the actuated button isrecognized. The meal rate 202 is not automatically delivered. This mustbe specially done each time a meal dosage is to be delivered to theuser. When a meal dose is needed, the M button is actuated and a "0"value is displayed on the LCD. The M button is then held actuated untilthe value on the LCD ramps up to the desired value by subroutine 206.When this desired value is reached, the M button is released and the Abutton is actuated. This will cause the apparatus to deliver the mealdosage from the apparatus to the user. At the completion of the deliveryof the meal dosage the apparatus will return to the 5 second waitroutine 176.

The following will be a description of the software associated with the5 second wait subroutine 176. When the apparatus is awakened at the endof every 5 second period, it leaves 5 second wait subroutine 176 andenters battery test subroutine 182. If the test is not satifactory,(primary batteries not present) the apparatus will go to Stop State 180and go to sleep state. Only after reinsertion of batteries will theapparatus wake up and battery reset condition 198 be completed and theapparatus will return to the 5 second wait subroutine.

If the battery test is successful, the apparatus will count out 12, 5second interrupts and then enter the 1 minute subroutine 184. In thistimekeeping mode, the apparatus only carries out or activates othersubroutines at 1 minute or 1 hour intervals. After 1 minute routine 184is entered, the real time clock 186 is updated by 1 minute. After 60 oneminute updates, the software enters hour subroutine 188. The hoursubroutine is for checking changed conditions of the apparatus, changein the basal profile 190, and for updating real time clock 186 by 1hour.

If there is a need for basal stroke, Need Basal subroutine 192 isentered either from new basal check subroutine 190 or from hoursubroutine 188.

If a basal stroke is not needed, the apparatus will return to 5 secondwait subroutine 176. If a basal stroke is needed, the apparatus willenter pump routine 194. However, before the routine causes any pumping,the apparatus enters HP (high pressure) check routine 191 to determineif the high pressure switch is closed. If it is closed, the apparatuswill enter HP set routine 193, which causes certain alarm conditions tobe set and the apparatus will return to 5 second wait subroutine 176. Ifwhen checked the HP switch is not closed, the apparatus will return topump routine 194 and cause pumping of fluid from the apparatus.

FIGS. 7, 8, 9a, and 9b show the engagement/disengagement means for leadscrew 242 for the apparatus of the invention. The lead screw is drivenby pump drive mechanism 12. Engagement/disengagement means 220 contactsplunger 5' which is part of the pumping system of the apparatus. Byforcing plunger 5' into reservoir 5, fluid is forced from the fluidreservoir to the user.

Referring to FIG. 7, an exploded view of engagement/disengagement meansfor lead screw 292 is generally shown at 220. The apparatus has a "U"shaped body 222. The body is comprised of first or center section 228having second section 224 disposed perpendicular to a first end of firstsection 228 and a third section 224 disposed perpendicular to the secondend of first section 228 with the second and third sections beingparallel to each other.

Second section 224 and third section of 226 have bores 230 and 231disposed therethrough, respectively. These bores are also in alignment.Another bore 232 is disposed through section 224, 226 and 228. This boreis for receiving therethrough lead screw 292. However, only a halfdiameter is cut into a surface of center section 228 such that leadscrew 292 would have half its diameter exposed when it is disposedthrough bore 232.

A third bore 234 is disposed partially through center section 228. Thisbore enters from the bottom surface of center section 228. The bore isused for disposition of spring 258, which will be describedsubsequently.

Engagement/disengagement means 220 has engaging member 236 which is of asize of that it will fit in the area between parallel second and thirdsections 224 and 226, respectively, of the "U" shaped body member 222.Bottom surface 237 of the engaging member 236 has a half diameter cutlongitudinally in it. This half diameter has threads 238, which arematched to the threads of lead screw 292. It is theengagement/disengagement of these threads which allows theengagement/disengagement means to operate in the desired fashion withlead screw 292.

Engaging means 236 has a first bore 240 disposed through it. Thecross-sectional shape of bore 240 has elongated sides 243 and 245 toallow interaction between member 236 and a shaft disposed therein. Bore240 also has a flat surface 242 disposed at the top of the bore. Thisbore is for receiving a portion of shaft 248 when means 220 isassembled.

Shaft 248 has a relieved portion having flat surface 250. The relievedportion is at least the length of bore 240 of engaging member 236. Theoperation of the relieved portion and the engaging member 236 will bedescribed subsequently.

Shaft 248 has a first end 252 which receives "E" ring 256. Shaft 248 isdisposed through bores 230, 240 and 231 when means 220 is assembled.Shaft 248 has a second end having a reduced diameter member 254. Thissecond end receives lever actuator means 272 such that bore 274 of thelever receives reduced diameter shaft 254 therethrough. Lever actuatormeans 272 has members 280 and 278 which are so disposed that slot 276 isformed between them for receiving a portion of plunger 5' (FIG. 2) ofthe pump mechanism for causing the pumping fluid from the fluidreservoir.

Engaging/disengaging member 220 has a bracket member 260. Bracket member260 has parallel side members 266 and 268 which are joined by bottommember 270. The side members are disposed perpendicular to bottom member270. On the ends of each side members 266 and 268, opposite the pointsof attachment to bottom member 270 are disposed lip members 262 and 264.These are disposed perpendicular to the respective side members,parallel to bottom member 270 and toward each other but their distalends are spaced apart.

When disposed on the apparatus, the bottom member 270 is biased againstspring 258 disposed in bore 234 of first section 228. Side members 266and 268 are disposed along opposite sides of body 222 with engagingmember 236 inserted therein and lip members 262 and 264 are disposed onsections 246 and 244 of engaging member 236 holding the bracket inplace. This configuration causes spring 258 to bias the bracket indownward direction B. This will in turn bias engaging means 236 which isin contact with bracket 260 toward lead screw 292 disposed in bore 232.

Referring to FIG. 8, an elevated view of the assembled apparatus isshown disposed on a lead screw 292. Lever actuator means 272 is shown inphantom rotated in a direction A. The resultant actions ofengagement/disengagement means 220 because of such rotation will bedescribed in conjunction with the disclosure of FIGS. 9A and 9B.

Referring to FIG. 9A, a cross-sectional view of engagement/disengagementmeans 220 is shown at 9--9 of FIG. 8. Referring to FIG. 9B, across-sectional view of engagement/disengagement means 220 shown in FIG.8 at 9--9 with the lever actuator means 272 rotated in direction A.

Again referring to FIG. 9A, when lever actuator means 272 is down, asshown in solid lines in FIG. 8, shaft 248 has the relieved portionhaving flat surface 250 facing up. In this position, flat surface 242 ofbore 240 is biased down against the relieved portion flat surface 250 bybiasing spring 258 that biases engaging member 236 in a downwarddirection B via bracket member 260. This will cause threaded portion 238of engaging member 236 to engage the threads of lead screw 292, therebyengaging engagement/disengagement means 220 such that means 220 and thelead screw 292 are in a screw/nut relationship.

Referring to FIG. 9B, when it is desired not to engageengagement/disengagement means 220 from lead screw 292 such that themeans 220 will freely slide up and down lead screw 292, lever actuator272 is rotated in direction A, as shown in FIG. 9B. When this takesplace, relieved portion having flat surface 250 of shaft 248 is rotatedout of contact with the flat portion 242 of bore 240 of engaging member236. This will cause flat portion 242 of bore 240 to now ride on theoutside diameter of shaft 248. This will cause the engaging member 236to move in direction C in opposition to biasing spring 258. This willdrive the threads 238 of engaging member 236 out of engagement with thethreads of lead screw 292. The means 220 can now freely slide up anddown lead screw 292. Engagement/disengagement means 220 is configured inthis manner so that when the fluid reservoir is empty or must be changedfor some other reason, the lever actuator 272 can be lifted or rotatedout of engagement with the threads of lead screw 292 and the means 220can be repositioned to receive the new reservoir and plunger.

Referring to FIGS. 10, 11, 12 and 13, pump drive mechanism 12 fordriving lead screw 292 for pumping fluid from the fluid reservoir 5 isshown.

Referring to FIG. 10 an exploded view of the mechanism is generallyshown at 300. The drive mechanism 300 is a solenoid drive apparatus forconverting electrical energy into the mechanical energy. Mechanism 300has outer housing 302 and leads 304 for receiving the output from powerstorage unit 10 shown in FIG. 3. The housing also has bores 306 and 307for receiving therethrough drive shaft 316 for driving lead screw 292through a coupling (not shown). Attached to an end of drive shaft 316 isratchet wheel 318 having teeth 319 disposed around the periphery.Housing 302 has disposed at one end spring stops 310 and 312. These arestops for springs 322 and 334, respectively. There is also a post 308which is for slidable attachment of first pawl 320 and rotatableattachment of second pawl 326, respectively. Slot 324 of first pawl 320is disposed on post 308 to allow for the linear movement of the pawl.

Pawl 320 works in conjunction with pawn 314, which extends from theinterior through the first end of housing 302, and spring 322. Thiscombination drives ratchet wheel 318 and resets pawl 320 as will bedescribed. Pawl 326 works in conjunction with driven pawl 320, spring334 and ratchet wheel 318. Pawl 326 is an antibacklash pawl, as will bedescribed subsequently. Finally, E-ring 336 is disposed on the end ofpost 308 to hold pawls 320 and 326 in place when the apparatus isassembled.

Referring to FIG. 11, the assembled solenoid drive mechanism 300 isshown generally at 340. The operation of the solenoid drive mechanism300 will be described referring to FIGS. 11, 12 and 13.

Referring to FIG. 12, a cross-sectional view of the mechanism is showngenerally at 350. The housing has two sections. First section 352 andsecond section 354 meet in a mating relationship.

Disposed in opening 353 within housing 302 is solenoid winding 356.Storage unit 10 (FIG. 3) will deliver its charge to solenoid winding 356and cause generation of the field which causes solenoid armature 358,disposed in bore 336 of second section 354 of housing 302, to be drivenin direction E. Surface 359 of solenoid armature 358, when the charge isdelivered, will be driven toward surfaces 360 of first section 352.Surface 360 in fact acts as a stop for surface 359.

When armature 358 moves in direction E, it will drive push rod 362having a first portion disposed in bore 368 and a second portiondisposed in a bore 370 in direction E since the tip of push rod extendsinto bore 336. This will cause the end of pawn 314 to move in directionD.

Referring to FIG. 13 when the above happens, pawl 320 having the end ofpawn 314 disposed in bore 325 will also be driven in direction D. Sincetip 323 of pawn 320 engages teeth 319 of ratchet wheel 318, the ratchetwheel will be driven in direction F. Likewise tip 330 of pawl 326, whichin a normal engagement position prior to movement of pawl 320, isdisposed one half the distance along one of the teeth 319 of ratchetwheel 318, will be caused to overcome that one tooth when pawl 320 isdriven in direction D. Pawl 326 with tooth 330 acts as an antibacklashdevice. Therefore, because of tooth 330 of pawl 326 the only backwardmovement of ratchet wheel 318 will be of a half a tooth distance in adirection counter to direction F.

Referring to FIG. 11, when tip 323 engages teeth 319 of ratchet wheel318 and driven in a direction D by pawn 314 disposed through a bore 325of pawl 320, spring 322 will be biased by pawn 320. When the charge isdepleted, spring 322 will force pawl 320 and pawn 314 back to theiroriginal positions. Likewise, once tip 330 of pawl 326 is lifted over atooth, spring 334 will extend and push it back to its original position,however tip 330 will be against the next tooth of ratchet wheel 318.This ratcheting will take place each time the charge is delivered to thesolenoid windings.

The terms and expressions which are employed here are used as terms ofdescription and not of limitation. And there is no intention in the useof such terms and expressions of excluding equivalence of the featureshown, and described, or portions thereof, it being recognized thatvarious modifications are possible in the scope of the invention asclaimed.

What is claimed is:
 1. A solenoid drive apparatus comprising:solenoidmeans responsive to applied electrical energy for moving a solenoidarmature in a first linear direction; a push rod mechanically linked tosaid solenoid armature to cause said push rod to be pushed in said firstlinear direction by the movement of said solenoid armature; a pawnhaving a base at one end thereof and a tip at an opposite end thereof, aportion of said base being in contact with said push rod, the movementof said push rod in said first linear direction thereby causing saidpawn to rock on said base, thereby causing said tip of said pawn to movein a linear motion in a second direction essentially orthogonal to saidfirst direction; a pawl mechanically engaged with said tip of said pawnand mounted for slideable movement in said second direction; a shafthaving a longitudinal axis parallel to said first direction, said pawlhaving one end thereof coupled to the circumference of said shaftwhereby the linear motion of said pawl in said second directiontranslates to rotational motion of said shaft to cause said shaft torotate; and means for allowing said shaft to rotate in one direction andfor preventing said shaft from rotating in the opposite direction.
 2. Asolenoid drive apparatus as defined in claim 1, additionallycomprising:means for biasing said pawl against movement in said seconddirection, said biasing means also causing said pawn to rock on its basein a direction opposite to the way said pawn is caused to rock bymovement of said push rod in said first linear direction.
 3. A solenoiddrive apparatus as defined in claim 2, wherein said biasing means is aspring.
 4. A solenoid drive apparatus as defined in claim 2, whereinsaid allowing means comprises:a second pawl, said second pawl allowingsaid shaft to rotate in one direction and preventing said shaft fromrotating in the opposite direction.
 5. A solenoid drive apparatus asdefined in claim 1, additionally comprising:a ratchet wheel mounted onthe end of said shaft, said pawl driving said ratchet wheel to causesaid ratchet wheel and said shaft to rotate.
 6. A solenoid driveapparatus as defined in claim 1, further comprising:biasing means forreturning said pawl, said pawn, and said push rod to positions they hadprior to the movement of said solenoid armature when said solenoid coilwas energized, said biasing means providing a biasing force which isovercome by the force of movement of said solenoid armature in saidfirst linear direction.
 7. A solenoid drive apparatus as defined inclaim 1, further comprisinga housing within which said solenoid means,said push rod, and said pawn are mounted, said shaft being mounted forrotation within said housing.
 8. A solenoid drive apparatus as definedin claim 7, wherein the rotation of said shaft controls the amount offluid delivered by an infusion pump, said solenoid drive apparatus beingmounted inside said infusion pump.
 9. A precision solenoid driveapparatus for a drug infusion pump, comprising:a housing; a pawn havinga base at one end thereof and a tip projecting from said base, said pawnbeing mounted in said housing for rocking motion with said said tip ofsaid pawn extending from one end of said housing; a pawl mechanicallyengaged with the tip of said pawn, said pawl being mounted on said oneend of said housing for movement in a second direction; means forbiasing said pawl against movement in said second direction, saidbiasing means causing said pawn to rock on its base; a solenoid windingdisposed within said housing and at the other end of said housing, saidsolenoid winding for being selectively energized and deenergized; asolenoid armature slideably mounted within said housing, said solenoidarmature being driven to move in a first linear direction when saidsolenoid winding is energized, said solenoid winding when energizedcausing said solenoid armature to exert force on said base of said pawnto cause said pawn to rock back on said base of said pawn, therebycausing said tip of said pawn and said pawl to to move in said seconddirection against said biasing means; means for translating saidmovement of said pawl in said first direction into rotational motion ofa shaft; and means for allowing said shaft to rotate in one directionand for preventing said shaft from rotating in the opposite direction.10. A solenoid drive apparatus as defined in claim 9, wherein saidallowing means comprises:a second pawl, said second pawl allowing saidshaft to rotate in one direction and preventing said shaft from rotatingin the opposite direction.
 11. A precision solenoid drive apparatus fora drug infusion pump, comprising:a housing; a pawn having a base at oneend thereof and a tip projecting from said base at an opposite endthereof, said pawn being mounted in said housing for rocking motion withsaid said tip of said pawn extending from one end of said housing; apawl mechanically engaged with the tip of said pawn, said pawl beingmounted on said one end of said housing for movmement in a seconddirection; means for biasing said pawl against movement in said seconddirection, said biasing means causing said pawn to rock on its base; asolenoid winding disposed within said housing and at the other end ofsaid housing, said solenoid winding for being selectively energized anddeenergized; a solenoid armature slideably mounted within said housing,said solenoid armature being driven to move in a first linear directiontoward said pawn when said solenoid winding is energized; a push rodlocated in said housing intermediate said solenoid armature and saidbase of said pawn, said push rod being mechanically linked to saidsolenoid armature to cause said push rod to be moved in said firstlinear direction by the movement of said solenoid armature, therebycausing said pawn to rock back on said base of said pawn, therebycausing said tip of said pawn and said pawl to move in said seconddirection essentially orthogonal to said first direction; a shaft havinga longitudinal axis parallel to said first direction, said shaft havinga ratchet wheel mounted thereon, said pawl having one end thereofcoupled to said ratchet wheel whereby the linear motion of said pawl insaid second direction translates to rotational motion of said ratchetwheel and said shaft to cause said ratchet wheel and said shaft torotate; and means for allowing said shaft to rotate in one direction andfor preventing said shaft from rotating in the opposite direction.